The present invention relates to a liquid development apparatus which carries out tonal density development per pixel for recording, and which uses a liquid developer for developing a latent image including half tone image parts so as to loyally develop the image with the use of micro toner particles in order to obtain a high quality developed image.
A liquid development apparatus, that is, a development apparatus using a liquid developer, can use micro toner particle toner having a particle size of less than 1 .mu.m, and accordingly, can effect such an advantage that a high quality image which is loyal to a latent image to be developed can be obtained. However, in the liquid development apparatus, a low density developer having a toner density of less than 1 mass % has to be used for obtaining a sufficient image density, and accordingly, a developer circulating system for feeding a large quantity of the developer to an image part, and also for promptly retrieving the developer after development should be required. Accordingly, the development apparatus has to be large-sized and complicated so as to be disadvantageous. Further, a density control mechanism for supplying the liquid developer has to be required in order to replenish for a decrease in the quantity of toner particles during development, and accordingly, it also cause the liquid development apparatus to be large-sized and complicated.
In order to miniaturize such a wet-type liquid development apparatus, it is required to eliminate the developer circulating system from the development apparatus while maintaining the supply of a developer sufficient to a latent image. Accordingly, it has been proposed that liquid developer having a toner density which is higher than that of a liquid developer usually used in a conventional liquid development apparatus, is used in order to supply toner sufficient to a latent image while reducing the supply volume of the liquid developer. AS to such prior art, for example, International Publication WO95/15516 (International Publication No. PCT/JP94/02034) discloses such a technology.
As disclosed in this document, a liquid development apparatus for developing a latent image formed in a photosensitive medium with the use of toner, has a development belt, and a layer forming blade for regulating the thickness of a highly viscous liquid developer layer which is applied on the development belt and in which toner is dispersed at a high degree of density. With this arrangement, the liquid development apparatus disclosed in this document can uniformly supply a small quantity of liquid developer having a high degree of density and a high degree of viscosity onto a latent image surface on an image forming medium.
However, in the above-mentioned conventional technology, there has been presented the following disadvantage. That is, a pre-wet applying device is required, in addition to the development apparatus, in this technology, since pre-wet liquid which is dielectric liquid having a releasable function and being chemically inactive is applied on a photosensitive medium serving as an image bearing medium in order to prevent a non-imaging part from fogging. Thus, the image forming apparatus has such a disadvantage that the number of components is increased so as to incur a high cost. In order to reduce the number of components in the apparatus so as to miniaturize the apparatus as a whole, there is required such an arrangement that occurrence of fogging can be prevented with no provision of a pre-wet applying device as incorporated in the above-mentioned image forming apparatus.
Further, Japanese Laid-Open Patent No. H7-334007 discloses a wet-liquid development apparatus in which a developer having a toner density of 5 to 70% is used, and which is composed of a development apparatus body having its top end opened and formed in a liquid tight box-like shape, developer liquid contained in the development apparatus body and a developing roller partly soaked in the developer liquid within the development apparatus body, facing the outer surface of a photosensitive drum and adapted to be rotated in a direction reverse to the rotating direction of the photosensitive drum.
However, in the above-mentioned conventional technology, there has been presented the following disadvantage. That is, the distance between the photosensitive drum and the developing roller has to be more precisely controlled as toner having a higher density is used in order to prevent occurrence of the so-called fogging in a part of a recording sheet, other than an image part. However, it is very difficult to ensure a high degree of accuracy for the distance therebetween, and further, a problem of higher cost is raised.
Japanese Laid-Open Patent No. H9-185264 discloses an image recording apparatus composed of a developer container reserving liquid developer in which charged toner particles composed of at least a coloring agent and resin is dispersed in electrically insulative liquid, a supply roller for feeding the liquid developer from the developer container to a developing roller whose outer surface is therefor stuck thereover with the liquid developer, and a field applying means for applying an electric field to the liquid developer stuck on the outer surface of the developing roller so as to form a liquid toner layer in which charged toner is concentrated. This liquid development apparatus carries out development on a belt type photosensitive medium on which a latent image is created, with the use of the developing roller holding thereon the liquid toner layer in which the charged toner is concentrated.
However, in the case of this conventional technology, there has also be presented the following disadvantage. That is, it is required to control the traveling speed of the belt type photosensitive medium and the rotating speed of the developing roller so as to be equal to each other in order to prevent occurrence of the so-called smearing phenomenon in the contact parts of the belt type photosensitive medium and the developing rollers, which is caused by the toner on the developing roller since the toner is rubbed by the belt type photosensitive medium. Thus, there has been raised a problem of high cost because it is very difficult to control the relative speed between the belt type photosensitive medium and the developing roller.